When an alkali metal dissolves in liquid ammonia the solution can acquire different colours. Explain the reasons for this type of colour change.

Explanation

The alkali metals dissolve in liquid `NH_3` and gives deep blue solutions. These are conducting in nature.
The blue colour of the solution is due to the ammoniated electrons which absorbs energy in the visible region of light and thus imparts blue colour to the solution.
These solutions are paramagnetic and on standing liberate hydrogen resulting in the formation of amide.
`M+(x+y)NH_3 to [M(NH_3)_x]^+ +[e(NH_3)_y]^-`
`M_((am))+e^(-)+NH_3 to MNH_(2(am))+1//2 H_2 (g)`
In concentrated solution the blue colour changes to bronze colour on warming and becomes did, magnetic.